LS-685/U Crystal Loudspeaker

Background

This military speaker is designed to be light weight. It
has a plastic case instead of the normal cast metal case and a
crystal speaker element instead of a classical coil and magnet
type speaker (typically with an audio transformer).

Description

Back of speaker

Front of speaker

Close up of front of speaker

Connector Markings

Opened Connector
A normal U-229 type plug has 3 pins in the metal
housing w/ 120 deg spacing, but the OCS66 shown
above has 4. The extra pin is shown at the top
center in the photo.

The LS-454/U speaker that was used
with the VRC-12 series VHF low
band radios used pins A (ground) and E (non standard) as does
this speaker. The common pins for an earphone or low power
speaker are A and B (see U229 Pin Out
web page).

The connector that looks similar to the common U-229 is in fact
a PCI OCS66 that seems to be designed to NOT mate with common
NATO audio connectors.

The speaker driver seems to be made up of a sandwich of three
layers: metallic cloth for one terminal, the piezo material in
the center and another layer of metallic cloth.

The speaker cone is a very stiff and light weight material,
maybe some type of fabric that's been stiffened, like fiberglass
or phenolic.

Questions

I got two of these and they are both dead.
They are alive, but need a new connector in order to test.

If you have a working speaker:
1) what DC resistance do you see across the terminals?
ans: The Fluke 87 DMM shows rising
resistance, i.e. a capacitor
2) what happens if you scrape a wire connecting a 1.5 Volt
Alkaline cell to the speaker terminals?
ans: At first contact there is a click, but
further contacts produce no sound.
Reversing the polarity causes one click, but no more with the
same polarity.
3) What equipment does the PCI OCS66 connector mate with?
ans: C11561 SINCGARS Full Size Remote

TM-11-5820-890-10-8 SINCGARS Ground Combat Net Radio ICOM Manual
says:
This is the only loudspeaker that can be used with the RCU speaker
connector.